U.S. patent application number 12/991298 was filed with the patent office on 2011-04-14 for device for the generation of microwaves.
Invention is credited to Magnus Karlsson, Fredrik Olsson.
Application Number | 20110084606 12/991298 |
Document ID | / |
Family ID | 41264763 |
Filed Date | 2011-04-14 |
United States Patent
Application |
20110084606 |
Kind Code |
A1 |
Olsson; Fredrik ; et
al. |
April 14, 2011 |
DEVICE FOR THE GENERATION OF MICROWAVES
Abstract
The invention relates to a device for the generation of
microwaves, comprising a virtual cathode oscillator (1) in coaxial
construction having an outer substantially cylindrical tube
constituting a cathode (2) and connected to a transmission
conductor (14) for feeding the cathode (2) with voltage pulses, as
well as an inner substantially cylindrical tube, at least partially
transparent for electrons, constituting an anode (3) and connected
to a wave guide (13) for the discharge of microwave radiation
generated by the formation of a virtual cathode (4) inside a region
enclosed by the anode. The device comprises an electrically
conductive structure in the form of a reflector (19) disposed
adjacent to the anode (3). The cathode (2) comprises a
substantially rotationally symmetric, electrically conductive body
(15) having a cavity (16). By configuring the cavity (16) in the
body (15) of the cathode with a first, lesser depth to that
boundary surface (18) of the body which is directly in front of the
peripheral part of the closure of the anode (3) against the
cathode, and a second, greater depth to the boundary surface (17)
of the body directly in front of the central part of the closure of
the anode (3) against the cathode, a device for the generation of
microwaves is produced, which has higher efficiency and high peak
power.
Inventors: |
Olsson; Fredrik; (Orebro,
SE) ; Karlsson; Magnus; (Karlskoga, SE) |
Family ID: |
41264763 |
Appl. No.: |
12/991298 |
Filed: |
April 16, 2009 |
PCT Filed: |
April 16, 2009 |
PCT NO: |
PCT/SE09/00191 |
371 Date: |
December 10, 2010 |
Current U.S.
Class: |
315/39.53 |
Current CPC
Class: |
H01J 25/74 20130101;
H01J 25/02 20130101 |
Class at
Publication: |
315/39.53 |
International
Class: |
H01J 23/36 20060101
H01J023/36 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2008 |
SE |
0801029-0 |
Claims
1. Device for the generation of microwaves. comprising a virtual
cathode oscillator in coaxial construction having an outer
substantially cylindrical tube constituting a cathode and connected
to a transmission conductor for feeding the cathode with voltage
pulses, as well as an inner substantially cylindrical tube, at
least partially transparent for electrons, constituting an anode
and connected to a wave guide for the discharge of microwave
radiation generated by the formation of a virtual cathode inside a
region enclosed by the anode, wherein an electrically conductive
structure in the form of a reflector is disposed adjacent to the
anode, and wherein the cathode comprises a substantially
rotationally symmetric, electrically conductive body having a
cavity, characterized in that the cavity in the body of the cathode
is configured with a first, lesser depth to that boundary surface
of the body which is directly in front of the peripheral part of
the closure of the anode against the cathode, and a second, greater
depth to that boundary surface of the body which is directly in
front of the central part of the closure of the anode against the
cathode.
2. Device according to Patent Claim I, characterized in that the
closure of the device against the cathode is disposed at a distance
to the boundary surface for the first, lesser depth of the body,
which distance is substantially equal to an odd multiple of the
quarter-wavelength for the microwaves to be generated.
3. Device according to Patent claim 2, characterized in that the
closure of the anode against the cathode is disposed at a distance
to the boundary surface for the first, lesser depth of the body,
which distance is substantially equal to a quarter-wavelength for
the microwaves to be generated.
4. Device according to claim 1, characterized in that the boundary
surface for the second, greater depth of the body is arranged at a
distance to the formed virtual cathode in the anode, which distance
substantially corresponds to an odd multiple of the
quarter-wavelength for the microwaves to be generated and is
greater than a quarter-wavelength.
5. Device according to claim 1, characterized in that the reflector
is disposed in the tube of the anode, which tube is at least
partially transparent for electrons, transversely to the
longitudinal direction of the tube at a distance from the virtual
cathode formed in the anode, which distance substantially
corresponds to an odd multiple of the quarter-wavelength for the
microwaves to be generated.
6. Device according to claim 1, characterized in that an
electrically conductive stop wall is disposed on the outer side of
the tube of the anode, which tube is at least partially transparent
for electrons, transversely to the longitudinal direction of the
tube at a distance which is substantially equal to an odd multiple
of the quarter-wavelength for the microwaves to be generated and is
greater than a quarter-wavelength from the boundary surface of the
cathode for the first, lesser depth.
7. Device according to claim 1, characterized in that the boundary
surface of the body for the lesser depth is configured with a
somewhat increasing depth in that part of the boundary surface
which lies at the radially greatest distance from the rotational
axis of the body.
8. Device according to claim 1, characterized in that the reflector
disposed adjacent to the anode comprises one or more electrically
conductive surfaces for partially filling a cross section of the
tubular anode.
9. Device according to claim 8, characterized in that the
electrically conductive surfaces of the reflector are constituted
by metal strips.
10. Device according to claim 8, characterized in that the
reflector is here configured with two opposite circle sectors
forming electrically conductive surfaces.
11. Device according to claim 8, characterized in that the
reflector is configured as a central strip forming an electrically
conductive surface.
12. Device according to claim 8, characterized in that the
reflector is configured with two strip sections separated in the
centre of the reflector and forming an electrically conductive
surface.
13. Device according to claim 1, characterized in that the
electrically conductive body of the cathode consists substantially
of aluminium.
14. Device according to claim 1, characterized in that the
transmission conductor for feeding of the cathode is connected to a
high-voltage generator.
15. Device according to claim 1, characterized in that the wave
guide for discharge of the microwave radiation is connected to an
aerial.
16. Device according to claim 15, characterized in that the aerial
is a horn aerial.
17. Device according to claim 2, characterized in that the boundary
surface for the second, greater depth of the body is arranged at a
distance to the formed virtual cathode in the anode, which distance
substantially corresponds to an odd multiple of the
quarter-wavelength for the microwaves to be generated and is
greater than a quarter-wavelength.
18. Device according to claim 3, characterized in that the boundary
surface for the second, greater depth of the body is arranged at a
distance to the formed virtual cathode in the anode, which distance
substantially corresponds to an odd multiple of the
quarter-wavelength for the microwaves to be generated and is
greater than a quarter-wavelength.
19. Device according to claim 4, characterized in that the boundary
surface for the second, greater depth of the body is arranged at a
distance to the formed virtual cathode in the anode, which distance
substantially corresponds to an odd multiple of the
quarter-wavelength for the microwaves to be generated and is
greater than a quarter-wavelength.
20. Device according to claim 2, characterized in that the
reflector is disposed in the tube of the anode, which tube is at
least partially transparent for electrons, transversely to the
longitudinal direction of the tube at a distance from the virtual
cathode formed in the anode, which distance substantially
corresponds to an odd multiple of the quarter-wavelength for the
microwaves to be generated.
Description
[0001] The present invention relates to a device for the generation
of microwaves, comprising a virtual cathode oscillator in coaxial
construction having an outer substantially cylindrical tube
constituting a cathode and connected to a transmission conductor
for feeding the cathode with voltage pulses, as well as an inner
substantially cylindrical tube, at least partially transparent for
electrons, constituting an anode and connected to a wave guide for
the discharge of microwave radiation generated by the formation of
a virtual cathode inside a region enclosed by the anode, wherein an
electrically conductive structure in the form of a reflector is
disposed adjacent to the anode, and wherein the cathode comprises a
substantially rotationally symmetric, electrically conductive body
having a cavity.
[0002] A device according to the first paragraph is essentially
previously known through "Microwave frequency determination
mechanisms in a coaxial vircator", Xupeng Chen et al, IEEE
Transactions on Plasma Science, Vol. 32, Issue 5, Oct. 2004, pp.
1799-1804.
[0003] Microwave generators of this kind can, inter alia, be used
to disable electronics by virtue of the high peak powers which can
be briefly generated, or to generate pulses in systems which
require high-power pulses for a short period.
[0004] A general problem with virtual cathode oscillators, often
termed "vircators" in English, is that they are low in efficiency.
There are therefore strong requirements to be able to improve the
efficiency of the device. Moreover, it may be valuable to be able
to increase the peak power and peak power efficiency of the
device.
[0005] One object of the present invention is to provide a device
for the generation of microwaves with improved efficiency. Another
object is to improve the peak power of the device. Since the
virtual cathode oscillator, the vircator, is primarily used to
create high-power microwave radiation, the peak power efficiency,
specifically, is a very important parameter.
[0006] The objects of the invention are achieved by a device for
the generation of microwaves according to the first paragraph,
characterized in that the cavity in the body of the cathode is
configured with a first, lesser depth to that boundary surface of
the body which is directly in front of the peripheral part of the
closure of the anode against the cathode, and a second, greater
depth to that boundary surface of the body which is directly in
front of the central part of the closure of the anode against the
cathode.
[0007] Through the introduction of a substantially rotationally
symmetric, electrically conductive body with divergent depth
relative to the closure of the anode against the cathode end, a
favourable interaction between anode and cathode has been realized,
resulting in increased efficiency and enhanced peak power
efficiency. The increase in efficiency and peak power has been able
to be verified by experiments and simulations.
[0008] Especially favourable improvements in efficiency and peak
power are obtained if the body of the cathode is dimensioned with
cavity and arrangement in relation to anode, reflectors and stop
walls such that, according to a preferred embodiment, the closure
of the device against the cathode is disposed at a distance to the
boundary surface for the first, lesser depth of the body, which
distance is substantially equal to an odd multiple of the
quarter-wavelength for the microwaves to be generated. In
particular, a compact construction is offered where the closure of
the anode against the cathode is disposed at a distance to the
boundary surface for the first, lesser depth of the body, which
distance is substantially equal to a quarter-wavelength for the
microwaves to be generated. By choosing the smallest odd multiple
of a quarter-wavelength, other distances which depend on this
distance for their dimensioning can be made short, resulting in a
compact device.
[0009] Further favourable improvements can be obtained if,
according to another preferred embodiment, the boundary surface for
the second, greater depth of the body is arranged at a distance to
the formed virtual cathode in the anode, which distance
substantially corresponds to an odd multiple of the
quarter-wavelength for the microwaves to be generated and is
greater than a quarter-wavelength.
[0010] In addition, according to another preferred embodiment, the
reflector can be disposed in the tube of the anode, which tube is
at least partially transparent for electrons, transversely to the
longitudinal direction of the tube at a distance from the virtual
cathode formed in the anode, which distance substantially
corresponds to an odd multiple of the quarter-wavelength for the
microwaves to be generated.
[0011] According to yet another preferred embodiment, an
electrically conductive stop wall is disposed on the outer side of
the tube of the anode, which tube is at least partially transparent
for electrons, transversely to the longitudinal direction of the
tube at a distance which is substantially equal to an odd multiple
of the quarter-wavelength for the microwaves to be generated and is
greater than a quarter-wavelength from the boundary surface of the
cathode for the first, lesser depth.
[0012] Advantageously, the boundary surface of the body for the
lesser depth is configured with a somewhat increasing depth in that
part of the boundary surface which lies at the radially greatest
distance from the rotational axis of the body. This slight increase
in the depression at the radially greatest distance contributes to
the favourable realization of distances specified for the device,
with respect to multiples of odd quarter-wavelengths.
[0013] A suitable reflector disposed adjacent to the anode
comprises one or more electrically conductive surfaces for
partially filling a cross section of the tubular anode. It is
especially proposed that the electrically conductive surfaces of
the reflector are constituted by metal strips. By virtue of the
proposed configuration of the reflector, which can be structurally
simple, a reflector with suitable balance between reflected and
transmitted microwaves is produced. According to a proposed
embodiment, the reflector is here configured with two opposite
circle sectors forming electrically conductive surfaces. According
to another embodiment, the reflector is configured as a central
strip forming an electrically conductive surface. According to a
further proposed embodiment, the reflector is configured with two
strip sections separated in the centre of the reflector and forming
an electrically conductive surface.
[0014] In an expedient embodiment, the electrically conductive body
of the cathode is proposed to consist substantially of aluminium.
The proposed material has the advantage of low weight and is
relatively easy to machine, for example by turning.
[0015] For feeding of the cathode of the device, a high-voltage
generator is expediently connected to the transmission conductor of
the cathode. In addition, the wave guide for discharge of the
microwave radiation is connected to an aerial. The aerial, it is
proposed, can be a horn aerial.
[0016] The invention will be described in greater detail below in
exemplified form with reference to the appended drawings, in
which:
[0017] FIG. 1 shows schematically an example of a known coaxial
virtual cathode oscillator forming part of a device for the
generation of microwaves,
[0018] FIG. 2 shows schematically in sectional view an example of a
coaxial virtual cathode oscillator according to the invention,
forming part of a device for the generation of microwaves,
[0019] FIG. 3 shows a more detailed example in sectional view of a
coaxial virtual cathode oscillator according to the invention,
forming part of a device for the generation of microwaves,
[0020] FIG. 4 shows schematically in block form a complete device
for the generation of microwaves, comprising a coaxial virtual
cathode oscillator according to the invention,
[0021] FIGS. 5a, 5b and 5c show schematically three examples of the
configuration of a reflector which can form part of the coaxial
virtual cathode oscillator shown in FIG. 2 or 3.
[0022] The known coaxial virtual cathode oscillator 1 which is
shown in highly schematic representation in FIG. 1 comprises a
cathode 2 in the form of an outer cylindrical tube and an anode 3
in the form of an inner cylindrical tube. The cathode oscillator is
of a very simple geometric design and is based on the fact that a
so-called virtual cathode 4 is formed inside the anode under
certain conditions.
[0023] FIG. 2 shows somewhat less schematically in longitudinal
cross section a modification of the known coaxial virtual cathode
oscillator for improving the efficiency and enhancing the peak
power. According to this embodiment, the cathode 2 is provided with
a rotationally symmetric body 15 having a cavity 16 and the shape
of the body can be most closely likened to the shape of a cup. The
cavity 16 is configured such that it has a greater depth in the
central parts of the body having a boundary surface 17, and a
lesser depth in the outermost part (viewed radially from the centre
of the body) having a boundary surface 18. The boundary surface 18
can in turn be divided into an inner part 18a of somewhat lower
depth than an outer part 18b.
[0024] A conductive structure in the form of a reflector 19 is
disposed in the interior of the anode. FIGS. 5a, 5b and 5c show
three examples of possible configurations of the reflector 19. The
reflectors comprise electrically conductive surfaces, which
partially fill the cross section shaped by the tubular interior of
the anode 3. According to the example in FIG. 5a, the conductive
surfaces form two diagonally opposing circle sectors 20, 21,
symmetrically centred with respect to a circle diameter 26. In FIG.
5b, the electrically conductive surface is constituted by a band
22, which is symmetrically centred with respect to the circle
diameter 26. In FIG. 5c, the electrically conductive surface is
constituted by two band sections 22a and 22b, which are
symmetrically centred with respect to the circle diameter 26 and
are separated from each other in the central part of the
surrounding circle 23. In FIGS. 5a and 5b, the circle diameter 26
is marked by means of a dashed line. The circle 23 surrounding the
conductive surfaces can be regarded as a mount for the conductive
surfaces. Alternatively, the circle can symbolize the inner
circumference of the tubular anode 3, in which the conductive
surfaces can be directly fastened in the cathode tube.
[0025] On the outer side of the tubular anode 3, there is disposed
a stop wall 24 consisting of an electrically conductive material,
such as aluminium or copper.
[0026] In the figure there are four different distances,
d.sub.1-d.sub.4, marked as follows:
[0027] d.sub.1 marks the distance between the boundary surface 18a
and the closure of the anode against the cathode,
[0028] d.sub.2 marks the distance between the stop wall 24 and the
boundary surface 18b,
[0029] d.sub.3 marks the distance between the boundary surface 17
and the virtual cathode 4 which is formed in the anode 3, and
[0030] d.sub.4 marks the distance between the virtual cathode 4 and
the reflector 19 disposed in the interior of the tubular anode.
[0031] The distances d.sub.1 to d.sub.4 are advantageously chosen
as follows:
d.sub.1=.lamda.*n/4, where n=1, 3, 5,
d.sub.2=.lamda.*n/4, where n=3, 5,7,
d.sub.3=.lamda.*n/4, where n=3, 5, 7
d.sub.4=.lamda.*n/4, where n=1, 3, 5,
with the secondary condition that d.sub.2 and
d.sub.3>d.sub.1.
[0032] The coaxial virtual cathode oscillator 1 can form part of a
device for the generation of microwaves shown in FIG. 4 and
comprising a high-voltage generator 7 connected to the input of the
cathode oscillator and an aerial 8 connected to the output of the
cathode oscillator. The aerial can be a horn aerial.
[0033] The cathode oscillator with peripheral arrangements is now
shown and described in greater detail with reference to FIG. 3,
both as regards configuration and working. Reference symbols having
correspondence in previously described figures have been denoted
with the same reference symbols in FIG. 3. According to FIG. 3, the
anode 3 and cathode 2 are disposed in a vacuum chamber 9 to which
there is a connection 10 for a vacuum pump (not shown). The anode 3
is provided with a grid 12, which is in part transparent for free,
electrically charged particles. The anode 3 passes into an outbound
wave guide 13, whilst the cathode 2 is fed via a transmission
conductor 14.
[0034] The design of the cathode oscillator is based on the fact
that a so-called virtual cathode is formed under certain
conditions. When a voltage pulse with negative potential is applied
via the transmission conductor 14 to the cathode 2, a highly
electrical field is created between the cathode 2 and the anode 3.
This results in electrons being field-emitted from the cathode
material. The electrons are subsequently accelerated towards the
anode structure and the majority of the electrons will also pass
through the anode and begin to be retarded. If certain conditions
are met, a virtual cathode 4 will be formed inside the anode
structure. Owing to the fact that the process is strongly
non-linear, phenomena occur which result in the generation of
microwave radiation. The more detailed preconditions for the
microwave generation are not described here, since this belongs to
the sphere of competence of a person skilled in the art. Under the
right preconditions, very high power is briefly generated in the
order of magnitude, typically, of 50-100 ns, before
short-circuiting occurs. Generated microwaves leave the anode of
the cathode oscillator via the wave guide 13 connected to the
anode, which has substantially the same radius as the anode 3. By
configuring the body 15 with a cavity 16 and boundary surfaces 17,
18 of varying depth in interaction with the anode 3, introducing
the reflector 19 and possibly the stop wall and, as far as
possible, applying the above-specified distance measurements with
respect to d.sub.1-d.sub.4, high-power pulses can be generated with
substantially improved efficiency and peak power.
[0035] The invention is not limited to the embodiments shown above
by way of example, but can be subjected to modifications within the
scope of the following patent claims.
* * * * *